Display screens are viewable from a wide angle and may be simultaneously viewed by a large number of viewers. However, in order to provide an adequate level of display intensity, a considerable amount of illumination power must be employed. Higher visibility of displays is achieved by pupil-forming projection displays. The delivery of the illumination to a limited exit pupil provides a number of advantages, such as display brightness and low external visibility. The display brightness is achieved by directing the principal part of the illumination to the exit pupil, and the low external visibility is achieved in the same way. The low external visibility precludes others, outside of the exit pupil, from viewing the display. This provides both security of information and provides dark surroundings around the exit pupil.
The problem with such pupil-forming projection displays has been that they have been limited to a single user because of the single exit pupil provided by their design. It is desirable to achieve the advantages of projection displays without necessarily limiting the viewpoint to a single exit pupil.